Permanent magnet type rotary electric machines, particularly small sized motors, generators and the like employing an arc-segment-shaped ferrite magnet have hitherto been widely used. Recently, the application of ferrite magnets has been extended to larger type motors. Particularly, such motors as a starter motor for driving an engine and a motor for driving a compressor in an air conditioner are, in many recent cases, subjected to heavy loads at the time of starting. In view of the strong demagnetizing field developed by the armature reaction in these motors, ferrite magnets having high resistance to demagnetization have been used. However, conventional ferrite magnets (particularly those used for starter motors) have in some cases been considerably demagnetized by an over current or by the starting current at low-temperature starting and, accordingly, are not satisfactory in terms of of reliability.
An example of a conventional permanent magnet type rotary machine has a cross sectional view as shown in FIG. 1. In the figure, a rotor 1 comprising an armature core (on which is provided an armature winding) and a commutator is supported by end brackets through bearings. A housing 2 supports permanent field magnets 31, 32. With this version of permanent magnet type rotary machine, there is an increasing demand for a more compact design, higher performance and higher output. For attaining a higher output, the permanent magnet used as the field magnet must have a higher residual flux density Br. On the other hand, enhancing the output is accompanied by an increase in the demagnitizing field developed by the armature reaction, giving rise to the need to use as the field magnet a permanent magnet having a higher coercive force .sub.I H.sub.C. Therefore, the use of a samarium-cobalt sintered permanent magnet having a coercive force .sub.I H.sub.C of about 15 kOe and a residual flux density of about 12 kG may be contempleted. This magnet, however, has the problem of high cost and poor mechanical strength (usually, a bending resistance on the order of 13 kg/mm.sup.2). It is also contempleted to use a ferrite produced from an inexpensive material, for example, a permanent magnet of sintered hexagonal lattice type oxide which has a basic composition consisting mainly of MO.nFe.sub.2 O.sub.3 (where M is selected from Ba, Si, Pb and Ca, or a mixture thereof; n is a number of 5 to 6), but with such material it is difficult to obtain an integrally formed permanent magnet having both a high residual flux density (Br) and a high coercive force (.sub.I H.sub.c) in combination. Thus, in cases of rotary machines with a conventional single-composition type permanent magnet used as field magnet, there have been certain limits on the improvement of performance, such as output, torque and resistance to demagnetization.
To overcome the limitations envolved in the conventional techniques, an improved permanent magnet field system for rotary machines has been proposed (Japanese Laid-Open Patent Publication No. 52-61712 entitled "Permanent Magnet Type Rotary Machine").
The present invention, based on further improvements to overcome the problems mentioned above, provides a composite type permanent magnet capable of exhibiting excellent properties for use as magnet for magnetic excitation and a method for producing the composite permanent magnet.